(1) Technical Field
The present invention relates generally to the production of purified liquids and vapors and more particularly to methods and apparatus for the separation of dissolved and/or trapped gasses from a liquid, as well as the production of high concentration vapors of the degassed liquid.
(2) Related Art
Liquids, whether occurring naturally or resulting from synthetic processes, oftentimes contain various constituents, in addition to the identified liquid material, as contaminants or by-products. Numerous methods are known for the extraction of many of these constituents. For example, appropriate reagents may be reacted with the constituents to form salts or other compounds that can then be removed by precipitation, centrifugation, filtering, etc. Similarly, sequestering agents may be used to sequester specific metal ions. Additionally, solvent extractions may be performed where the identified liquid is “washed” with an incompatible liquid that has a greater solubility or affinity for the constituent. Finally, the liquids may be subjected to simple filtering methods using filters, such as HEPA filters or activated carbon filters, having particular efficacy or affinity for the material to be removed.
While such methods will “purify” the liquid of many undesired constituents, oftentimes such liquids still retain dissolved or trapped gasses. The presence of such constituents is not always problematic. However, certain manufacturing processes require high purity materials. This is particularly true in the field of microelectronics, where many techniques or processes, such as chemical vapor deposition (CVD), molecular beam epitaxy (MBE), ion implantation, plasma etching, and gas mixing, use source materials that are liquids at room temperature and require heating to produce a vapor. Current vapor delivery systems utilize bubblers, vaporizers, high pressure nozzles etc., which are difficult to handle, have an initial delay (warm up and settling time), and require particular equipment modifications.
For example, U.S. Pat. No. 5,814,819 to Sinclair et al. teaches the use of water vapor in neutralizing an ion beam in an ion implanter. Ion implantation is particularly important in semiconductor/integrated circuit manufacture. Similarly, U.S. Pat. No. 6,248,642 to Dolan et al. teaches the use of a controlled water vapor for oxygen implantation in the production of silicon wafers. Traditionally, water vapor for these processes is generated by heating the water above its boiling point or by subjecting water to ultrasonic vibrations that create a fine mist of water. While both methods produce the desired water vapor, care must be taken to avoid condensation of the water on the materials being implanted or the equipment used in such processes. Such condensation may occur as a result of the low pressures (below atmospheric pressure) employed in carrying out ion implantation. Furthermore, neither of these methods of generating water vapor removes or prevents the presence of extraneous gases or constituents in the water vapor, both of which can adversely affect the performance of ion implantation processes, increasing the defect rate in the resultant products.
Thus, there exists a need for methods and apparatus for providing purified liquids free of, or substantially free of, dissolved and/or trapped gaseous constituents. There also exists a need for methods and apparatus for readily producing highly concentrated vapors of such purified liquids, especially at low pressures, i.e., below atmospheric pressure. Finally, there exists a need for simple methods and apparatus for forming a highly-saturated, purified, low pressure water vapor.